This invention relates to a centrifugal classifier comprising a housing, which is provided with inlets for material to be classified and for classifying air or with an inlet for material to be classified and for classifying air and with outlets for a mixture of classifying air and fines and for coarses, and at least one rotor, which essentially consists of an annular series of blades and is movably mounted in the housing. Such classifier are already known from German Patent Publication No. 1757 582 or from German Patent Specification No. 29 51 819.
In the known classifiers the rotor shaft is movably mounted in the housing or frame by means of sliding surface bearings or rolling element bearings. The bearings must be lubricated and must be protected from an ingress of particles. On the other hand, an ingress of lubricant particles into the product must be prevented. For this reason the bearings must carefully be separated from the set of rotor blades and from the production space proper and must be sealed or encapsulated. Said measures are expensive. In particular, they add to the weight of the machine and involve a larger space requirement, particularly in an axial direction. In the conventional design the shaft is movably mounted in two axially spaced apart bearings, which are disposed outside the housing between the basket of the classifier and the drive. The shaft must be sealed where it extends through the housing in order to prevent a sucking of extraneous air from the outside and an ingress of foreign particles. That seal between the housing and the shaft increases the distance between the basket of the classifier and the bearing on the outside of the housing so that the thickness of the shaft is increased and two axially spaced apart bearings are required to ensure the required stability.
In view of the above it is an object of the invention to provide centrifugal separators which are of the kind defined and in which a separate seal between the shaft and the housing is not required and a shorter shaft may be used so that their axial extent is reduced.
How that object can be accomplished is as follows: The rotor shaft is movably mounted in the housing, particularly in the end wall of the housing, by means of at least one bearing that is adapted to be swept by a fluid and serves also as a seal between the rotor and the housing. A separate seal is not required due to the fluid which is required for the operation of the bearing and the ambient atmosphere. It will be understood that the fluid is compatible with the working fluid or with the product contained in the interior of the housing and usually consists of air or an inert gas. The fluid may be supplied in a liquid state and may be evaporated in the sealing or bearing gap so that the bearing is cooled at the same time.
Numerous further designs and variations may be adopted. A single bearing, which is disposed between the rotor blade basket and the drive and is mounted in the end wall of the housing, may be sufficient. Alternatively, one bearing mounted in the end wall of the housing may be supplemented by another bearing, which may be a conventional lubricated bearing or also a lubricant-free fluid bearing. In the latter case, both bearings may be mounted in a common bearing housing so that the seal against the ambient atmosphere is effected in two stages and is thus facilitated.
In a further embodiment, a bearing between the rotor shaft and the end wall of the housing is provided as well as a further lubricant-free bearing, which is disposed between the outlet for fines and classifying air and an end ring of the rotor.
In a particularly compact arrangement the drive motor is accommodated in a motor housing, which is axially attached to the housing of the classifier or the motor is flanged to said motor housing and two lubricant-free bearings are provided, which consist of a bearing disposed between the basket of the classifier and the motor and a second bearing mounted on that end wall of the motor housing which is remote from the basket of the classifier. In that case the rotor of the motor is additionally cooled and protected from foreign matter by the sealing fluid.
Aerostatic or inert gas-static bearings may be used as well as electromagnetic bearings which are flown through by a sweeping or sealing fluid. Whereas electromagnetic bearings are more expensive, an electric motor drive may be integrated in or attached to the electromagnetic bearing.
It may be pointed out that the invention may be utilized to the same advantage not only in centrifugal classifiers but also in other machines in which a rotor must movably be mounted in the housing in such a manner that the rotor is sealed from the housing and from internal fixtures in the housing, on the one hand, and from the ambient atmosphere, on the other hand. This will be applicable to fans and blowers as well as to pumps for handling certain fluids without contamination.